KADUNA, Nigeria, July 23 (Reuters) - At least 82 people were killed on Wednesday in two bombings in the northern Nigerian city of Kaduna targeting opposition leader and former president Muhammadu Buhari at a busy market and a moderate Muslim cleric about to lead a crowd in prayer.

The attacks bore the hallmarks of Islamist group Boko Haram but may also have been linked to politics ahead of 2015's elections.

The deadlier blast targeted Buhari's convoy at the crowded Kawo market, his son told Reuters on the scene. A Red Cross official said at least 50 people were killed there.

Buhari was the main opposition party contender against President Goodluck Jonathan in the 2011 election and remains a key figure in the opposition alliance. He was riding in an armour plated sports utility vehicle and was not wounded.

A crowd gathered at the scene of the incident, until the military dispersed them by firing shots in the air. Smoke rose from another vehicle destroyed in the blast.

Earlier, a suicide bomber targeting a moderate cleric killed at least 32 of his congregation on a busy commercial road.

Thousands were gathered for prayers with Sheikh Dahiru Bauchi in Murtala Muhammed square, and when his convoy pulled up, the bomber lunged at him before being stopped by his private security, witnesses and police commissioner Shehu Umar Ambursa said.

Kaduna's governor Mukhtar Yero declared a 24 hour curfew on the city until further notice and condemned the bombs as "the height of cowardice".

"The enemies of peace have visited us with their ungodly venom of wanton destruction," he said in a statement. "Those behind the act have no notion of God, as they have none for the sanctity of human life."

The bomber did not injure Bauchi, several witnesses told Reuters. Mustafa Sani, a volunteer for Bauchi's mosque evacuating bodies, said there were 32 confirmed dead so far.

"Somebody with a bomb vest ... was blocked. He detonated the bomb along with the person that tried to block him," the police commissioner said, adding police had been able to confirm 25 dead, with 14 wounded. Police sometimes give lower casualty tolls than workers on the scene.

The military used pick-up trucks to cordon off the area. Sirens wailed as fire engines raced to the scene.

An angry crowd started throwing stones at police, who responded with teargas. Some followers had come from Senegal, Chad and Niger to see the popular sheikh.

BOKO HARAM SUSPECTED

There was no immediate claim of responsibility for either blast, but Islamist militant group Boko Haram has been staging attacks, especially with explosives, outside its northeastern heartlands for the past three months.

Buhari and his political team did not immediately react.

The main Islamic association Jama'atu Nasril Islam called the bombs "acts of terror" and said Nigeria was becoming "a theatre of lost of blood for no just cause".

Since launching an insurgency in 2009, the militants have often attacked clerics, such as Bauchi, who take issue with their Salafist ideology. If Boko Haram is responsible for Wednesday's attack, it underscores the risks moderate clerics take speaking out against it.

The insurgents, who are fighting to carve out an Islamic state in Nigeria, have repeatedly targeted civilians, mostly in remote northeastern Borno state. They killed more than 2,000 civilians during the first half of this year, Human Rights Watch estimated a week ago.

The Islamists attacked the northeastern town of Damboa and surrounding villages over the weekend, killing at least 50 people.

The rebellion has been in the international spotlight since Boko Haram fighters kidnapped more than 200 girls from a school in the northeastern village of Chibok on April 14. Jonathan met parents of the abducted girls, and some other girls who had escaped, for the first time on Tuesday.

Boko Haram leader Abubakar Shekau last week claimed responsibility for two explosions on June 25 at a fuel depot in Lagos, Nigeria's commercial hub, that killed at least two people.

A military offensive since May last year that was meant to dismantle their hold on the northeast has caused the militants to react in two ways: brutal attacks on civilians in the region have surged dramatically, and efforts to strike out in areas far from the rebels' strongholds have resumed.

A blast in the central city of Jos, 170 km (105 miles) east of Kaduna, killed 118 people in May. (Writing and additional reporting by Tim Cocks; Editing by Alison Williams)

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